The use of a metered dose inhalation (MDI) apparatus for administering medicaments into the lungs of a patient is well known. In order to effectively channel the medication from the MDI canister to the mouth and subsequently into the lungs of the user, a variety of devices, generically known as "spacers", have been developed to accept an MDI canister dispenser and condition its output for entry into the lungs.
A preferred form of such a spacer, which provides a dynamic mixing chamber for the medication, is that illustrated and claimed in U.S. Pat. No. 5,040,527 to the present inventors. That patent discloses and claims a spacer in which the MDI output as directed away from the mouthpiece of the device. A first, low-level air flow is developed by the user's inspiratory breath through the spacer, in a direction opposed to the release of the medication, through a first air inlet. Simultaneous with the activation of the MDI dispenser and release of the medication spray, the opposed inspiratory air flow is increased by the opening at a second air inlet. The increased flow contacts the spray plume to cause a high level of mixing and a decrease in spray particle size, resulting in an efficient draw of the spray medication into the lungs of the user.
In the disclosed embodiment the duration of the increased air flow, which draws the medication into the lungs, is dependent upon the length of time which the MDI dispenser is depressed. Although the MDI dispenser releases a metered amount of spray independently of the depression time, depression of the dispenser maintains the opening of the second air inlet and thus the time during which increased air flow can be maintained. In certain cases, particularly with users having insufficient hand strength or dexterity, the MDI dispenser may not be able to be held down for a sufficient period, resulting in premature closing of the second air inlet and thus reducing the amount of the medication dose swept from the spacer volume.
It is accordingly a purpose of the present invention to provide a spacer apparatus which allows the onset of increased air flow to coincide with actuation of the MDI dispenser, but allows the flow to continue irrespective of continued actuation of the dispenser after the medication is dispensed.
Another purpose of the present invention is to provide a spacer of the aforementioned type in which increased airflow is generated by the opening of air inlet ports, the ports remaining open and exposed after actuation of the MDI dispenser.
Yet a further purpose of the present invention is to provide an MDI spacer which does not rely on a continuing manually applied force to control the duration of the increased air flow.
Still another purpose of the present invention is to provide a MDI spacer which generates a timed increased airflow which can be easily reset for a subsequent use, and which is economical and efficient to manufacture and use.